White Manna is a very popular place, and you are likely to see this no matter what time you visit the tiny little diner as people cram inside the door to place their orders. The interior is focused entirely (laughably so) on the grill in the middle where everyone watches their meat sizzle. The long road to getting your well done sliders ($1.10 or $1.30 w/ cheese, below) is on full display, organized on the grill by the cook who seems to retain a steady focus throughout. Try to get his attention and break his concentration and he will deflect your questions to the others. A fun game!
As stated, the sliders come well done, and as far as I know there is no other option. I think they cook them too long, but maybe that is a good idea. The pickles they serve with the burgers are best added to give the little things some life. After simmering on the grill for that long, the bun, cheese, onions, and meat all seem to become one by the time you receive them.
The experience here is great though, and with such cheap prices there is an obvious formula to the popularity that spans many decades.